Thermal infrared observations of Cepheid envelopes with VLT/VISIR

We present here our recent results obtained using the mid‐infrared imaging instrument VISIR at the ESO VLT. Using a combination of short exposures and “lucky imaging,” we obtained diffraction limited (for an 8 m telescope) images of Cepheids. We detected circumstellar envelopes (CSE) both photometrically and spatially, at a fraction of an arcsecond scale. These CSE, most probably due to mass loss, represent a significant bias to distance determination using Baade‐Wesselink methods and using surface brightness of interferometric method. This observational study is part of multi instruments/technics effort we are carrying over to detect and characterize CSE.